Etching a laser-cut semiconductor before dicing a die attach film (DAF) or other material layer

ABSTRACT

Semiconductor die break strength and yield are improved with a combination of laser dicing and etching, which are followed by dicing an underlying layer of material, such as die attach film (DAF) or metal. A second laser process or a second etch process may be used for dicing of the underlying layer of material. Performing sidewall etching before cutting the underlying layer of material reduces or prevents debris on the kerf sidewalls during the sidewall etching process. A thin wafer dicing laser system may include either a single laser process head solution or a dual laser process head solution to meet throughput requirements.

TECHNICAL FIELD

This disclosure relates to laser processing systems and methods. Inparticular, this disclosure relates to laser processing systems andmethods for micromachining (e.g., scribing or dicing) semiconductordevices.

BACKGROUND INFORMATION

Integrated circuits (ICs) are generally fabricated in an array on or ina semiconductor substrate. ICs generally include one or more layersformed over or in the substrate. The one or more overlying layers may beremoved along scribing lanes or streets using a mechanical saw or alaser. After scribing, the substrate may be throughcut, sometimes calleddiced, using a saw or laser to separate the circuit components from oneanother.

When laser processing is used, the results tend to be highly materialdependent. For example, a first laser type (or set of laser parameters)may be ideal for cutting semiconductors, while a second laser type (orset of laser parameters) may be ideal for cutting metals.

One example of a challenging problem is the singulation of semiconductordevices mounted on die attach film (DAF), a process sometimes referredto herein as “DAF dicing.” This problem may be addressed in productionby using mechanical diamond saws with ultra-thin blades because laserdicing with known processes tend to produce a die with lower mechanicalstrength compared to that produced by mechanical sawing. Incorporationof fragile low-k dielectric materials into these semiconductor devicesalong with reduction of the silicon wafer thickness has increased thedifficulty for mechanical saw dicing, leading to slower throughputs andmore yield losses. Using a traditional laser-only process for DAF dicingof thin silicon wafers also typically results in increased die pickfailure (reduced die yield) manifested as, for example, uncut DAF(“double die”), overcut DAF (“anchoring”), and/or low die break strength(due to etch variance when etching after laser dicing the DAF).

Previously attempted solutions for DAF dicing include using lasers toscribe the low-k dielectric and/or semiconductor layers prior tomechanical saw dicing, combining laser dicing with a post-dicing etchprocess to strengthen the die, using a full-cut laser dicing system withtwo different lasers (or different sets of laser parameters such aspulse width), or freezing the DAF and stretching it until the tapefractures. A known method for dicing through both the semiconductordevice and the DAF using a single laser dicing strategy results in adeposition of DAF material on the sidewalls of the semiconductor diessuch that a subsequent xenon difluoride (XeF₂) etch process is adverselyaffected by this “DAF splash.”

SUMMARY OF THE DISCLOSURE

In one embodiment, a method dices a semiconductor wafer that including atop surface and a bottom surface. The bottom surface is attached to anunderlying layer of material. The method includes generating a firstlaser beam, and providing relative movement of the first laser beam withrespect to the top surface of the semiconductor wafer to at leastpartially dice the semiconductor wafer from the top surface along one ormore dicing streets. The first laser beam forms a kerf defined bysidewalls in the semiconductor wafer. The method further includesetching the sidewalls of the at least partially diced semiconductorwafer to reduce or remove a heat affected zone (HAZ) produced in thesidewalls by the first laser beam, and cutting through the underlyinglayer of material along the one or more dicing streets so as to separatea die from the semiconductor wafer having at least a predetermined diebreak strength and to produce a yield of operational die that equals atleast a predetermined minimum yield. The sidewall etching is performedbefore the cutting through the underlying layer of material to reduce orprevent debris on the sidewalls from the underlying layer of materialduring the etching of the sidewalls.

In certain embodiments of the method, the underlying layer of materialincludes a die attach film (DAF). In such embodiments, cutting throughthe underlying layer of material includes generating a second laserbeam, and providing relative movement of the second laser beam withrespect to the DAF along the one or more dicing streets. The first laserbeam may include a pulsed laser beam having an ultraviolet (UV)wavelength and with nanosecond or picosecond temporal pulsewidths. Thesecond laser beam may include a pulsed laser beam having a visiblewavelength and with nanosecond temporal pulsewidths.

In certain other embodiments, etching the sidewalls includes using afirst etchant configured to remove semiconductor material from thesemiconductor wafer, and cutting through the underlying layer ofmaterial includes using a second etchant configured to remove the DAFmaterial. In one embodiment, the first etchant includes a spontaneousetchant, such as xenon difluoride (XeF₂). Plasma etching, wetphotoresist strip, or wet etching techniques may be used to cut throughthe DAF.

In certain embodiments, the top surface includes one or more devicelayers including a pattern of multiple, mutually spaced apart electroniccircuit components separated by one or more streets. The method furtherincludes, before generating the first laser beam, applying a coating tothe semiconductor wafer to protect the semiconductor wafer from debrisgenerated by the first laser beam, in a first pass of the first laserbeam along the one or more dicing streets, scribing the one or moredevice layers, and after at least partially dicing the semiconductorwafer in a second pass of the first laser beam along the one or morestreets, and before etching the sidewalls, washing the semiconductorwafer to remove the coating.

In certain embodiments, the underlying layer of material includes ametal. In certain such embodiments, cutting through the underlying layerof material includes generating a second laser beam, and providingrelative movement of the second laser beam with respect to the metalalong the one or more dicing streets. In other such embodiments, cuttingthrough the underlying layer of material includes using a second etchantconfigured to remove the metal.

In one embodiment, a laser processing system dices a semiconductor waferincluding a top surface and a bottom surface. The bottom surface isattached to an underlying layer of material. The system includes a firstlaser processing head for generating a first laser beam, and forproviding relative movement of the first laser beam with respect to thetop surface of the semiconductor wafer to at least partially dice thesemiconductor wafer from the top surface along one or more dicingstreets. The first laser beam forms a kerf defined by sidewalls in thesemiconductor wafer. The system further includes a first etch stationfor etching the sidewalls of the at least partially diced semiconductorwafer to reduce or remove a heat affected zone (HAZ) produced in thesidewalls by the first laser beam, and a dicing station for cuttingthrough the underlying layer of material along the one or more dicingstreets so as to separate a die from the semiconductor wafer having atleast a predetermined die break strength and to produce a yield ofoperational die that equals at least a predetermined minimum yield. Thefirst etch station performs the sidewall etching before the dicingstation cuts through the underlying layer of material to reduce orprevent debris on the sidewalls from the underlying layer of materialduring the etching of the sidewalls.

In certain system embodiments, the first laser processing head includesa first laser source for generating ultraviolet (UV) laser pulses withnanosecond or picoseconds temporal pulsewidths.

In certain system embodiments, the first etch station uses a spontaneousetchant to remove semiconductor material from the sidewalls of thesemiconductor wafer. The spontaneous etchant may include xenondifluoride (XeF₂).

In certain system embodiments, the underlying layer of material includesDAF, and the dicing station includes a second laser processing headincluding a second laser source for generating a second laser beamcomprising visible laser pulses with nanosecond temporal pulsewidths forcutting the DAF.

In certain system embodiments, the underlying layer of materialcomprises a metal backing, and the dicing station includes a secondlaser processing head including a second laser source for generating asecond laser beam for cutting the metal backing.

In certain system embodiments, the underlying layer of material includesDAF, and the dicing station includes a second etch station for cuttingthrough the DAF.

In certain system embodiments, the underlying layer of material includesa metal backing, and the dicing station includes a second etch stationfor cutting through the metal backing.

In certain embodiments, the system further includes a coating station,before the first laser processing head, for applying a protectivecoating to the semiconductor wafer. Such embodiments may further includea wash station, after the first laser processing head and before thefirst etch station, for removing the protective coating along withdebris from the semiconductor wafer.

Additional aspects and advantages will be apparent from the followingdetailed description of preferred embodiments, which proceeds withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates a top view of a workpiece that includesa semiconductor wafer mounted on a dicing tape disposed in a wafer ring.

FIG. 2A is a scanning electron microscope (SEM) micrograph of siliconwith DAF diced using a full cut laser process, before sidewall etching.

FIG. 2B is an SEM micrograph of the silicon with DAF shown in FIG. 2A,after sidewall etching.

FIG. 3 is a graph of measured die break strengths for three siliconwafers.

FIG. 4 is an SEM micrograph of a die that is diced according to oneembodiment.

FIG. 5 is a flowchart of a process for dicing a semiconductor waferaccording to one embodiment.

FIGS. 6A, 6B, 6C, 6D, and 6E schematically illustrate cross-sectionaldiagrams of a workpiece during different steps of a dicing processaccording to certain embodiments.

FIG. 7 is a flowchart of a process for dicing a workpiece including adevice stack formed in or on a silicon substrate having a back or bottomsurface affixed to DAF according to one embodiment.

FIG. 8 is a block diagram of a system for dicing a semiconductor waferhaving a surface attached to an underlying layer of material accordingto one embodiment.

FIGS. 9A, 9B, 9C, and 9D schematically illustrate side perspective viewsof a semiconductor wafer including a metal backing being diced accordingto certain embodiments.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Systems and methods disclosed herein provide a laser dicing solutionthat reduces or eliminates problems caused by material splashing ontosemiconductor sidewalls. The disclosed embodiments provide a higheryield (e.g., higher die break strength) and a higher die pick percentagethan those provided by conventional full laser cut systems.

Although many of the examples herein are directed to thin wafer dicing,and in particular to dicing a semiconductor material attached to a dieattach film (DAF), other embodiments include dicing a workpiece thatincludes a semiconductor layer adjacent to a layer comprising any othermaterial that may splash onto the sidewalls of the semiconductor. Forexample, certain embodiments provide dicing of a workpiece that includesa semiconductor layer adjacent or attached to a metallic layer.

According to certain embodiments, a thin wafer dicing laser system mayinclude either a single laser process head solution or a dual laserprocess head solution to meet throughput requirements of about 15 wafersper hour (WPH) for wafers that are less than about 50 μm thick, havingdiameters of about 300 mm, and with die sizes of about 10 mm×10 mm.Artisans will recognize from the disclosure herein that any other wafersize and/or die size may also be processed using the embodimentsdisclosed herein.

A first process laser head, according to one embodiment, includes asingle nanosecond or picosecond ultraviolet (UV) laser. Depending on theparticular target material processed by the single process laser head,other types of lasers may be used. For example, an infrared (IR) orgreen laser may be used. The laser may be a diode-pumped solid-statelaser, a mode-locked laser, or any other laser suitable for machiningthe semiconductor and other materials of the wafer. Beam positioning maybe controlled using, for example, galvanometers and a telecentric scanlens to cut a tooling path along a dicing lane or street. Each scanfield or region may be scribed, followed by semiconductor (e.g.,silicon) dicing, before an XY stage is indexed to a next scan field.

Certain embodiments also use a second process laser head. The laser ofthe second process laser head is selected to process a material adjacentto the semiconductor. For example, the laser of the second process laserhead may include a low cost nanosecond laser with a visible wavelengthused to cut the DAF. As another example, the laser of the second processlaser head may include a pulsed or continuous wave (CW) laser with a UV,green, or IR wavelength (e.g., a CO₂ laser) used to cut metal.

In certain embodiments, a method of dicing a semiconductor waferattached to an underlying layer of material (e.g., DAF or metal backing)includes at least partially dicing the semiconductor wafer using a laserbeam, etching the sidewalls to reduce or remove a heat affected zone(HAZ), followed by cutting through the underlying layer of material withthe same laser beam or a different laser beam. An etchant for sidewalletching of the semiconductor wafer may be, but is not limited to, aspontaneous etchant such as xenon difluoride (XeF₂). In certainembodiments, other types of etching, such as wet chemical etching orplasma etching, may also be used.

Cutting through an underlying material such as DAF or metal backingtends to produce debris or splash on the sidewalls that can reduce theeffectiveness of the etch process to remove the HAZ. Thus, performingthe sidewall etching before cutting through the underlying layer ofmaterial reduces or prevents debris or splash on the sidewalls such thatthe sidewall etching process is more effective.

In certain other embodiments, a method of dicing a semiconductor waferattached to an underlying layer of material (e.g., DAF or metal backing)includes at least partially dicing the semiconductor wafer using a laserbeam, etching the sidewalls to reduce or remove a heat affected zone(HAZ), followed by cutting through the underlying layer of material witha second etching process. For example, after sidewall etching of thesemiconductor wafer using a spontaneous etchant, plasma etching, wetphotoresist strip, or wet etching may be used to etch through the DAF.As another example, for embodiments where the underlying layer ofmaterial is a metal backing, the metal in the dicing street may be cutthrough using lithography and plasma etching. Table 1 provides examplesof plasma etching specific chemistries for etching metal or othermaterials used for the underlying layer of material.

Example Materials Etched by Corresponding Gas Systems

TABLE 1 Material(s) Processed Etch Chemistry Reaction Products Si CF₄,SF₆, HBr, Cl₂, NF₃, HI SiF₄, SiCl₄, SiF₂, SiCl₄, SiBr₄, Sil₄ SiO₂, Si₃N₄CHF₃, C₄F₈, C₂F₆, SF₆, NF₃ SiF₄, CO, CO₂ Al BCl₃, HCl, Cl₂ Al₂Cl₆, AlCl₃W SF₆, CF₄, NF₃, Cl₂, O₂ WF₆, WOCl_(x) Ti, TiN Cl₂ TiCl₄ Polymers O₂,O₂/CF₄, SO₂ CO, H₂S, CO₂, HF, H₂, H₂0 InP, HgCdTe CH₄/H₂ In(CH₃)₃, PH₃,Cd(CH₃)₂ GaAs Cl₂, BCl₃ Ga₂Cl₆, AsCl₃

The embodiments disclosed herein increase die yield and die strengthacross the wafer, improve standard deviation and process stability, andimprove die pick as a direct result of DAF cutting. The disclosedembodiments may also reduce the consumption of etchant used for sidewalletching, which may result in a lower cost of ownership (CoO), lower costper wafer, and added tool value.

Reference is now made to the figures in which like reference numeralsrefer to like elements. In the following description, numerous specificdetails are provided for a thorough understanding of the embodimentsdisclosed herein. However, those skilled in the art will recognize thatthe embodiments can be practiced without one or more of the specificdetails, or with other methods, components, or materials. Further, insome cases, well-known structures, materials, or operations are notshown or described in detail in order to avoid obscuring aspects of theembodiments. Furthermore, the described features, structures, orcharacteristics may be combined in any suitable manner in one or moreembodiments.

FIG. 1 schematically illustrates a top view of a workpiece 100 thatincludes a semiconductor wafer 110 mounted on a dicing tape 112 disposedin a wafer ring 114. A top surface (shown in FIG. 1) of thesemiconductor wafer 110 is divided into a plurality of semiconductorchips 116 along scribe lines or streets 118. The semiconductor chips 116include electronic circuit components formed on or in one or more devicelayers (also referred to herein as a “device stack”) of thesemiconductor wafer 110. A bottom surface (not shown) of thesemiconductor wafer 110 may include a die attach film (DAF) that servesas an adhesive at the time of mounting the semiconductor chips 116 to awiring substrate (not shown). The DAF may comprise a polymer. By way ofexample only, and not by limitation, DAF materials are available fromHitachi (e.g., FH-900) or from Nitto (e.g., EM-500 or EM-700).

FIG. 2A is a scanning electron microscope (SEM) micrograph of silicon210 with DAF 212 diced using a full cut laser process, before sidewalletching. As discussed above, an unetched laser-cut sidewall 214(a) shownin FIG. 2A includes a heat affected zone (HAZ) that reduces themechanical strength of the die. The HAZ may be removed through sidewalletching. FIG. 2B is an SEM micrograph of the silicon 210 with DAF 212shown in FIG. 2A, after sidewall etching. FIG. 2B shows the depositedDAF “splash” 216 on the etched sidewall 214(b). The DAF deposit or DAFsplash 216 impedes the etching process (e.g., using XeF₂) and reducesthe die strength of the silicon wafer 210. At least a portion of the DAFsplash 216 in FIG. 2B is tilting or falling off the etched sidewall214(b) because the silicon attached to a portion of the DAF splash 216has been etched away. Thus, the DAF splash 216 is lifting off the etchedsidewall 214(b) and may be at least partially hinging at the interfaceof the silicon 210 and the DAF 212.

FIG. 3 is a graph of measured die break strength for three siliconwafers. The illustrated data (mean die strength, maximum die strength,and minimum die strength) was measured using a three-point die strengthtest on blank 75 μm silicon (Si) wafers (with and without DAF). A firstcolumn 310 shows data for a first silicon wafer without DAF that hasbeen laser diced, but which has not been etched. A second column 312shows data for a second silicon wafer without DAF that has been laserdiced and etched. A third column 314 shows data for a third siliconwafer with DAF that has been laser diced through both the silicon andthe DAF before being etched. In this example, the DAF is FH-900available from Hitachi. As shown, the minimum die strength for the thirdwafer is lower than the minimum die strength of the second wafer becauseDAF splash prevents the etching process from sufficiently removing theHAZ, which allows micro cracks to propagate through the silicon whenstress is applied.

Those skilled in the art will recognize that a three-point bendingtechnique may be used to generate a fracture across a silicon wafer.Generally a three-point die strength test includes placing a siliconwafer between two supports and asserting a force in the middle of thewafer. The force at which the wafer fractures is measured and used in aknown three-point bending formula that includes the thickness of thesilicon wafer, the width of the silicon die/sample, and the span betweenthe two supports. The formula calculates a stress per unit area of thesilicon wafer. Thus, the mechanical strength of the die may bedetermined for various laser processing techniques.

FIG. 4 is an SEM micrograph of a die 400 that is diced according to anembodiment disclosed herein. FIG. 4 shows a top surface 410 of the die400 and an etched silicon sidewall 412. Although not shown, in certainembodiments one or more device layers may be formed on or in the topsurface 410 and/or the top surface 410 may be covered with a photoresistor other coating material. The silicon sidewall 412 is formed by laserdicing the silicon from the top surface 410 down to a bottom surface(not shown) of the silicon, which is attached to a layer of DAF 414.Before cutting the DAF 414, the silicon sidewall 412 is etched forstress relief (e.g., to remove HAZ created by laser processing thesilicon). Following the sidewall etching, a second laser process is usedto dice the DAF 414. In addition, or in other embodiments, the etchedsilicon sidewall 412 is coated (e.g., with parylene or other polymer) toprotect the etched silicon sidewall 412 during the second laser processand/or during subsequent processing steps.

FIG. 4 also shows a DAF lip or flap 416 created by widening the siliconsidewall 412 during the sidewall etching process. For clarity, a DAF lipor flap 630 is also shown in FIG. 7E. In certain embodiments, thesidewall etching process is controlled such that the size of the DAF lipor flap 412 allows the second laser process to cut the DAF 414 withoutinterference from (or interfering with) the etched silicon sidewall 412.After dicing the DAF 414, in the example shown in FIG. 4, the DAF lip orflap 416 for the die 400 is about 18.5 μm wide. After the silicon is atleast partially diced and etched along a street between the die 400 andan adjacent die (not shown), the distance between silicon of the die 400and the adjacent die determines the accuracy for aligning the laser beamalong the street during the second laser process. The size of theresulting DAF lip or flap 416 may be determined by the spot size andother parameters of the laser beam during the second laser process. Inembodiments where the DAF 414 is removed in a second etching process,rather than in a second laser process, the DAF lip or flap 416 may bereduced or completely removed.

FIG. 5 is a flowchart of a process 500 for dicing a semiconductor waferaccording to one embodiment. The semiconductor wafer includes a topsurface and a bottom surface. The bottom surface is attached to anunderlying layer of material. In certain embodiments, the underlyinglayer of material includes DAF. In other embodiments, the underlyinglayer of material includes, for example, metal. The method 500 includesusing 510 a first laser beam to at least partially dice thesemiconductor wafer. In certain embodiments, the first laser beamremoves a sufficient amount of semiconductor material so as to at leastpartially expose a surface of the underlying layer of material along adicing street. In other embodiments, the first laser beam only partiallydices the semiconductor material along the street such that theunderlying layer of material is not exposed. In such embodiments,leaving a thin layer (e.g., about 1 μm to 3 μm or more) of semiconductorover the underlying layer of material decreases the likelihood splashingthe underlying layer of material onto the sidewalls of the semiconductorbefore the etching process.

The method 500 further includes etching 512 the sidewalls of the atleast partially diced semiconductor wafer to reduce or remove HAZproduced in the sidewalls by the first laser beam. Then, the method 500includes cutting 514 through the underlying layer of material along theone or more dicing streets so as to separate a die from thesemiconductor wafer having at least a predetermined die break strengthand to produce a yield of operational die that equals at least apredetermined minimum yield. The predetermined die break strength andthe predetermined minimum yield depend on the particular application.For example, a bare/mirror SiO2 wafer, according to one embodiment, hasa predetermined die break strength of about 500 MPa. In addition, or inother embodiments, the predetermined minimum yield is in a range between99.5% and 100%. The sidewall etching is performed before the cuttingthrough the underlying layer of material to reduce or prevent debris onthe sidewalls from the underlying layer of material during the etchingof the sidewalls. The cutting of the underlying layer of material may beperformed using either a second laser beam or a second etchantconfigured to remove the underlying layer of material along the one ormore dicing streets.

FIGS. 6A, 6B, 6C, 6D, and 6E schematically illustrate cross-sectionaldiagrams of a workpiece 600 during different steps of a dicing processaccording to certain embodiments. The workpiece 600 includes a devicestack 610 formed over a semiconductor (e.g., silicon) wafer 612. In thisexample, DAF 614 is affixed to a back or bottom surface of thesemiconductor wafer 612. The device stack 610 may include electroniccircuit components including one or more device layers formed on or in atop surface of the semiconductor wafer 612. The one of more devicelayers of the device stack 610 may include, for example, silicon dioxide(SiO₂) and/or silicon-nitride (Si_(Y)N_(X)) (e.g., Si₄N₃) used forpassivation and/or encapsulation, one or more metallic layers separatedby dielectric layers (e.g., SiN), and/or a low-k dielectric layer.

As shown in FIG. 6B, a first laser beam 616 scribes the device stack 610to expose the underlying semiconductor substrate 612 along a dicingstreet 617. In FIG. 6C, a second laser beam 618 at least partially dicesthe semiconductor wafer 612. In one embodiment, the first laser beam 616and the second laser beam 618 are generated by different laser sourcesand/or have different laser parameters. In another embodiment, the firstlaser beam 616 and the second laser beam 618 shown in FIG. 6C representdifferent passes of the same laser beam along the dicing street 617. Inyet other embodiments, both the device stack 610 and at least a portionof the semiconductor wafer 612 are cut along the dicing street 617 in asingle pass of a single laser beam. As discussed above, although thesecond laser beam 618 in FIG. 6C appears to remove a sufficient portionof the semiconductor wafer 612 so as to expose the underlying DAF 614,certain embodiments leave a few microns of semiconductor material overthe DAF 614 to reduce or prevent splashing of the DAF 614 onto thesidewalls 620 of the semiconductor wafer 612 before etching.

FIG. 6D represents the sidewall etching step. In FIG. 6D, the originalsidewalls 620 formed by the second laser beam 618 in FIG. 6C arerepresented as dashed lines. The sidewall etching step removes a portionof the original sidewalls 620 (e.g., a portion including HAZ) to formetched sidewalls 622.

In FIG. 6E, a third laser beam 624 dices the DAF 614 so as to separate afirst die 626 from a second die 628. In one embodiment, the second laserbeam 618 and the third laser beam 6624 are generated by different lasersources and/or have different laser parameters. In another embodiment,the second laser beam 616 and the third laser beam 618 representdifferent passes of the same laser beam along the dicing street 617. Asshown in FIG. 6E, processing the DAF 614 using the third laser beam 624results in the DAF lip or flap 630 discussed above with respect to FIG.4. In other embodiments, a second etching step is used instead of thethird laser beam 624 to cut through the DAF 614. Such embodiments mayreduce or eliminate the DAF lip or flap 630.

FIG. 7 is a flowchart of a process 700 for dicing a workpiece includinga device stack formed in or on a silicon substrate having a back orbottom surface affixed to DAF according to one embodiment. The process700 includes coating 710 the workpiece with a protective coating toprotect against debris from scribing and dicing processes. Theprotective coating may include a liquid resin (e.g., silicon glycolcopolymer). As described above, the process 700 further includes devicestack scribing 712 followed by silicon laser dicing, which at leastpartially dices the silicon substrate but may leave a few microns ofsilicon over the DAF along a dicing street. The method 700 furtherincludes washing 716 the workpiece to removing the protective coating.The workpiece may be washed with, for example, deionized water oranother solvent. The process 700 also includes etching 718 sidewalls ofa kerf cut into the silicon substrate during the laser dicing. Afteretching 718, the process 700 includes DAF dicing 720. Performing the DAFdicing 720 after the etching 718 reduces or avoids the presence of DAFon the sidewalls during the etching 718, which increases the ability ofthe etching 718 to reduce or remove HAZ so as to increase die breakstrength. Performing the DAF dicing 720 after the etching 718 alsoreduces or prevents splashed DAF from hinging or falling from thesidewalls during later processing (e.g., packaging).

FIG. 8 is a block diagram of a system 800 for dicing a semiconductorwafer having a surface attached to an underlying layer of materialaccording to one embodiment. In certain embodiments, the underlyinglayer of material includes DAF. In other embodiments, the underlyinglayer of material includes, for example, metal. The system 800 includesa first cassette 810, a coating station 812, a first laser processinghead 814, a wash station 816, an etch station 818, a second laserprocessing head 820, and a second cassette 822. Skilled persons in theart will recognize from the disclosure herein that the system 800 inother embodiments may include fewer elements (e.g., a single cassetteand/or a single laser processing head) or additional elements.

The first cassette 810 may include a carrier configured to hold a stackof semiconductor wafers that can be sequentially loaded (e.g., by arobot) for dicing by the system 800. The coating station 812 may spin aprotective coating 710 onto a semiconductor wafer to protect againstdebris from scribing and dicing processes. The first laser processinghead 814 includes a laser source for generating a first laser beam and amotion stage for providing relative movement of the first laser beamwith respect to the top surface of the semiconductor wafer to at leastpartially dice the semiconductor wafer from the top surface along one ormore dicing streets. The first laser beam forms a kerf defined bysidewalls in the semiconductor wafer. The wash station 816 then removesthe protective coating along with any debris produced by the first laserbeam.

The etch station 818 etches the sidewalls of the at least partiallydiced semiconductor wafer to reduce or remove a heat affected zone (HAZ)produced in the sidewalls by the first laser beam. Then, the secondlaser processing head 820 cuts through the underlying layer of materialalong the one or more dicing streets so as to separate a die from thesemiconductor wafer having at least a predetermined die break strengthand to produce a yield of operational die that equals at least apredetermined minimum yield. Performing the sidewall etching beforecutting through the underlying layer of material reduces or preventsdebris on the sidewalls from the underlying layer of material during theetching of the sidewalls. Finally, the die is loaded into the secondcassette 822 for further processing. In certain embodiments, the secondlaser processing head 820 is replaced with a second etch stationconfigured to cut through the underlying layer of material usingetching, as discussed herein. Thus, the second laser processing head 820may be referred to as a “dicing station.”

FIGS. 9A, 9B, 9C, and 9D schematically illustrate a side perspectiveview of a workpiece 900 including a metal backing 914 being dicedaccording to certain embodiments. The workpiece 900 includes one or moredevice layers 910 formed over a semiconductor wafer 912 (e.g., silicon).In this example, metal 914 is affixed to the back surface of thesemiconductor wafer 912.

As shown in FIG. 9B, a dicing process includes a first pass of a laserbeam 916 along a street 918 of the workpiece 900 (e.g., using an X-Ytranslation stage that provides relative motion of the laser beam 916 inthe direction of the arrow with respect to the street 918). The firstpass of the laser beam 916 scribes the workpiece 900 by removing the oneor more device layers 910 so as to expose the underlying semiconductorwafer 912 along the street 918. The laser parameters used for the firstpass of the laser beam 916 may be configured to process a combination ofmetals (e.g., copper) and low-k dielectrics in the street 918 of the oneor more device layers 910. In an example embodiment, a UV or green lasersource is used to generate the laser beam 916 for the first pass withpulses having temporal pulse durations in a range between about 12 nsand about 14 ns.

A next step of the dicing process, as shown in FIG. 9C, includes asecond pass of the laser beam 916 along the street 918 to cut throughthe semiconductor wafer 912. During the second pass, the laser beam 916may be generated by the same UV or green laser source to provide laserpulses having temporal pulse durations in a range between about 1nanoseconds and about 3 nanoseconds. Although not shown, the sidewallswithin the street 918 are then etched. Following the sidewall etching, anext step of the dicing process, as shown in FIG. 9D, includes a thirdpass of the laser beam 916 along the street 918 to cut through the metal914. In the third pass, according to one embodiment, the laser beam 916has a velocity with respect to the workpiece 900 in a range betweenabout 100 mm/s and about 4,000 mm/s, a pulse repetition rate in a rangebetween about 1 kHz and about 1 MHz, a spot size in a range betweenabout 4 μm and about 12 μm, pulse energy in a range between about 10 μJand about 1,000 μJ, and a UV wavelength in a range between about 352 nmand about 355 nm. In another embodiment, in the third pass, the laserbeam 916 has a green wavelength (e.g., about 532 nm. In yet anotherembodiment, in the third pass, the laser beam has an IR wavelength(e.g., as produced by a CO₂ laser). Persons skilled in the art willrecognize from the disclosure herein that other types of lasers or laserparameters may be used for each of the three passes.

It will be understood by those having skill in the art that many changesmay be made to the details of the above-described embodiments withoutdeparting from the underlying principles of the invention. The scope ofthe present invention should, therefore, be determined only by thefollowing claims.

The invention claimed is:
 1. A method for dicing a semiconductor waferincluding a top surface and a bottom surface, the bottom surfaceattached to an underlying layer of material, and the top surfacecomprising one or more device layers including a pattern of multiple,mutually spaced apart electronic circuit components separated by one ormore streets, the method comprising: applying a coating to thesemiconductor wafer to protect the semiconductor wafer from debrisgenerated by a first laser beam; generating the first laser beam;providing relative movement of the first laser beam with respect to thetop surface of the semiconductor wafer to: in a first pass of the firstlaser beam along one or more dicing streets, scribe the one or moredevice layers; and in a second pass of the first laser beam along theone or more streets, at least partially dice the semiconductor waferfrom the top surface along the one or more dicing streets, the firstlaser beam forming a kerf defined by sidewalls in the semiconductorwafer; washing the semiconductor wafer to remove the coating; etchingthe sidewalls of the at least partially diced semiconductor wafer toreduce or remove a heat affected zone (HAZ) produced in the sidewalls bythe first laser beam; and cutting through the underlying layer ofmaterial along the one or more dicing streets so as to separate a diefrom the semiconductor wafer having at least a predetermined die breakstrength and to produce a yield of operational die that equals at leasta predetermined minimum yield, the sidewall etching being performedbefore the cutting through the underlying layer of material to reduce orprevent debris on the sidewalls from the underlying layer of materialduring the etching of the sidewalls.
 2. The method of claim 1, whereinthe underlying layer of material comprises a die attach film (DAF). 3.The method of clam 2, wherein cutting through the underlying layer ofmaterial comprises: generating a second laser beam; and providingrelative movement of the second laser beam with respect to the DAF alongthe one or more dicing streets.
 4. The method of claim 3, wherein thefirst laser beam comprises a pulsed laser beam having an ultraviolet(UV) wavelength and with temporal pulsewidths selected from the groupcomprising nanosecond temporal pulsewidths and picosecond temporalpulsewidths.
 5. The method of claim 4, wherein the second laser beamcomprises a pulsed laser beam having a visible wavelength and withnanosecond temporal pulsewidths.
 6. The method of claim 2, whereinetching the sidewalls comprises using a first etchant configured toremove semiconductor material from the semiconductor wafer, and whereincutting through the underlying layer of material comprises using asecond etchant configured to remove the DAF material.
 7. The method ofclaim 6, wherein the first etchant comprises a spontaneous etchant. 8.The method of claim 7, wherein the spontaneous etchant comprises xenondifluoride (XeF₂).
 9. The method of claim 6, wherein the second etchantcomprises an oxide etchant.
 10. The method of claim 1, wherein theunderlying layer of material comprises a metal.
 11. The method of claim10, wherein cutting through the underlying layer of material comprises:generating a second laser beam; and providing relative movement of thesecond laser beam with respect to the metal along the one or more dicingstreets.
 12. The method of claim 10, wherein etching the sidewallscomprises using a first etchant configured to remove semiconductormaterial from the semiconductor wafer, and wherein cutting through theunderlying layer of material comprises using a second etchant configuredto remove the metal.